oops. cracker.

[Lumpy]

Checking and cleaning wheels and brakes today to find a crack in the left disc. Aaagh. Drilled a hole at the end to stop further extension. New discs ordered today. Bugger.

[Skippernick]

lucky you checked though.

[darrsi]

You only need one, they work independently!!

[Lumpy]

You only need one, they work independently!!

indeed but I always replace in pairs
Same as pads.

[bozboz]

Lumpy are you keeping your old right disc or would you be willing to sell it? Unless thats cracked too...

[darrsi]

Out of curiosity, what discs did you go for?

[Lumpy]

Lumpy are you keeping your old right disc or would you be willing to sell it? Unless thats cracked too...

rs is fine. Just usual wear. I would keep it but if you need it you can have it.

[Lumpy]

Out of curiosity, what discs did you go for?

good question. Made up in Coventry. I'll have a look. Outgoings were Kazagum8 or summit and have been fine for 2 years plus.

[bozboz]

[quote author=bozboz link=topic=5646.msg49864#msg49864 date=1356744691]
Lumpy are you keeping your old right disc or would you be willing to sell it? Unless thats cracked too...

rs is fine. Just usual wear. I would keep it but if you need it you can have it.
[/quote]
Cheers Lumpy, sent you a PM 

[darrsi]

[quote author=darrsi link=topic=5646.msg49866#msg49866 date=1356745911]
Out of curiosity, what discs did you go for?

good question. Made up in Coventry. I'll have a look. Outgoings were Kazagum8 or summit and have been fine for 2 years plus.
[/quote]


That's what i'm using at the moment, the wavy one's, they've been very good and are noticeably thicker than most other discs.

[Lumpy]

That's what i'm using at the moment, the wavy one's, they've been very good and are noticeably thicker than most other discs.

been fine on mine. All weathers. Loads a miles. Never a problem. Well up until just now. Always yes true. Always good braking. Not bad wear either. Hopefully the Brit made ones will be better tho.

[Lumpy]

Further oops. Replaced same day with Zone Products discs, new pads, and new pins.

[His Dudeness]

2 years out of a brake disk is pretty crap. lucky you spotted it. a crack that big could have caused a serious accident

[Lumpy]

2 years out of a brake disk is pretty crap. lucky you spotted it. a crack that big could have caused a serious accident

oh yes, if it had peeled away it would have been character builing. The showed signs of wear with the original pads but the EBCs and Vesrahs were better. The cost of non-OEM discs I guess. They were in pretty good nick for 30k in all weathers even after the very aggresive first set of pads. No idea why it cracked, I'm not that hard on them really. The crack started on the outside and came in, there has been no knocks or bangs on it, it wasn't twisted either. Who knows. The repeated heating and cooling must have work hardened it maybe.

[His Dudeness]

probably fatigue failure. maybe caused by a flaw in the material that wasn't visible on the surface. here's a bit about it  http://en.wikipedia.org/wiki/Fatigue_%28material%29

[markbubble]

thats good job you spotted before it locked up on you or something. what bolts are you using to hold discs on?i thought they were always held on with allen headed bolts(that can be a pain to remove) hope yours are correct stress related etc

[limax2]

I've had a Zone Products disc on the back for about 5,000 mile now. Still looking good.

[Lumpy]

thats good job you spotted before it locked up on you or something. what bolts are you using to hold discs on?i thought they were always held on with allen headed bolts(that can be a pain to remove) hope yours are correct stress related etc

the screws are proper grade SS 302 or 304 (I forget) to match the 8.8s standard. Some of the screws were damaged getting them out the last time and I fitted these to all 12. I have fitted washers under the heads this time to save graunching the carriers and need to fit the dome headed bolts on the LS to clear the speedo drive.

I will get some new disc screws I think and do all 12. What you need is a good fitting Allen socket, not key, and grease the bolts upon insertion and torque them correctly. Most people overtighten them and that leads to destroying the hex with an ill fitting key when taking them out. If I took the washers out from under them the hex screws clear the speedo drive okay.

I use titanium ones on the other bike but won't invest that on this one but a new standard set for the front maybe, although they are fine as is.

[Lumpy]

probably fatigue failure. maybe caused by a flaw in the material that wasn't visible on the surface. here's a bit about it  http://en.wikipedia.org/wiki/Fatigue_%28material%29

It's more likely to be caused by a stress raiser and the many heating and cooling cycles with a touch of work hardening. Due to the type of material used and the manner of manufacture the likelihood of a flaw is remote, although possible. There was definitely something other than use that caused it. Maybe the heat treatment during manufacture wasn't done correctly, maybe a stone hit it square on causing a little nick. I noticed this disc was showing slight corrosion around the periphery where the other side wasn't. Still, this is all conjecture and I am just pleased that it was found and wasn't a catastrophic failure

[unfazed]

Reason for that crack is simple looking at the corrosion on the discs and fork legs.
The rivets/bobbins which allow the disc to float have seized from the buildup of corrosion.When they seize the disc cannot move as it should when it expands/contracts and its only option to allow its movent is to crack at the weakest point, which it has.
The pictures also show the disc bolts have been replaced with standard bolts and washers.
When you replace the 2 discs, replace the bolts with the proper ones and overhall the calipers at the same time. With that level of corrosion it is possile the capipers are close to seizing point.